In connection with a cutting technique of a pipe, as the size and weight of pipes gradually increase, orbital cutting apparatuses are being developed, in which a cutting tool performs cutting while rotating around and peeling the outer circumference of a fixed pipe little by little by a predetermined depth. Such an orbital cutting apparatus for a pipe is now capable of performing chamfering and cutting by being equipped with both of a cutting tool and a chamfering tool.
As an example of an orbital cutting/chamfering apparatus as described above, an apparatus illustrated in FIGS. 1 and 2 (hereinafter, referred to as “Prior Art 1”) has been disclosed. As illustrated in FIGS. 1 and 2, Prior Art 1 includes a main body 10 configured to fix a pipe material P positioned at the center thereof. When the pipe material P passes through any one side (front side) of the main body 10, a rotary body 20 configured to be rotated by an electric motor 15 is coupled to the pipe material P. A cutting tool 31 and a chamfering tool 32 are mounted at the front side of the rotary body 20 to be opposite to each other (or two or more tools to be balanced) such that the cutting tool 31 and the chamfering tool 32 are configured to move vertically (toward the center of the pipe material) by a predetermined depth whenever the rotary body 20 rotates once. Here, the cutting tool 31 and the chamfering tool 32 are mounted on a block 40, which is guided to be capable of reciprocating toward the center of the pipe material P on the front face of the rotary body 20, and the blocks 40 are screw-coupled to a rotary shaft 50, of which the upper end is formed with a gear 51. Accordingly, whenever the gear 51 comes in contact with a finger stop 60 protruding from the main body 10, the rotary shaft 50 vertically moves the block 40 by a pitch corresponding to the rotating angle of the gear 51 so as to make the cutting tool 31 and the chamfering tool 32 move forward to the center of the pipe material P.
As described above, Prior Art 1 is related to an apparatus that is capable of cutting the pipe material or simultaneously cutting and chamfering the pipe material by causing the cutting tool 31 and the chamfering tool 32 to dig into the pipe material P by a predetermined depth whenever the cutting tool 31 and the chamfering tool 32 revolve around the pipe material one round, but is a limited technique that cannot arbitrarily control the movements of the cutting tool and the chamfering tool. That is, Prior Art 1 cannot arbitrarily adjust the cutting tool and the chamfering tool while the rotary body 20 is being moved.
When the cutting tool and the chamfering tool cannot be adjusted, it means that cutting conditions cannot be changed depending on the size, material, kind, or the like of a workpiece. This may naturally deteriorate the cutting efficiency, and may also disable cutting itself. In addition, there will be a trouble in that in order to return the cutting tool and the chamfering tool to the original positions thereof after the cutting operation is completed, it is necessary to reversely rotate the rotary body again or to perform an operation for returning the rotary body to the original position thereof using a separate reverse rotating means.
In addition, in the case of the cutting/chamfering apparatus of Prior Art 1, it is difficult to anticipate when the cutting tool and/or the chamfering tool become dull or are damaged so that workpieces may be frequently damaged due to the damage of the cutting tool and/or the chamfering tool. That is, in a case where a tool is in a dull or damaged state in the cutting/chamfering apparatus of Prior Art 1, the tool continuously digs into the workpiece by the rotation of the gear even though the workpiece is in a non-cut state due to the abnormal condition of the tool. As this state is repeated, load increases between the tool and the workpiece so that the load may cause the entire tool or the workpiece to be damaged.
In addition, the cutting/chamfering apparatus has problems in that it is impossible to process various shapes, it is impossible to cut a pipe material having a thickness that is thicker than a predetermined thickness, a damage may be caused by a collision between the gear and the finger stop, a cutting depth may not be adjusted, and a chamfering edge should be frequently replaced depending on a chamfering angle and shape. However, the problems are not solved.
These problems will be described in more detail with reference to a case in which Prior Art 1 processes a pipe material in an operating sequence as illustrated FIG. 3. That is, the cutting tool 31 and the chamfering tool 32 dig into the pipe material P as illustrated in the first drawing in FIG. 3, and processing is performed while causing the cutting tool 31 and the chamfering tool 32 to gradually and more deeply dig into the pipe material P in the order as illustrated in the second to fourth drawings so that the pipe material P is chamfered simultaneously with being cut. Accordingly, the processing of the pipe material by Prior Art 1 has a limit in that the processing capable of being performed by Prior Art 1 is confined to cutting as illustrated in FIG. 4A and cutting and one side chamfering as illustrated in FIG. 4B.
As illustrated in FIG. 5, it is natural that the cutting tool 31 for use in cutting a pipe material should have a length that is long as compared to the thickness t of a pipe material to be cut in order to cut the pipe material. However, when the length L of the cutting tool is increased in order to cut a pipe material having a thickness t of dozens of mm or more, the cutting tool may not withstand the force applied thereto and may thus be easily damaged.
In addition, as illustrated in FIG. 6, it is natural that the length lb of the edge of the chamfering tool 32 for improving and processing a cut surface of a pipe material should be longer than the length of an inclined surface of the pipe material. However, as illustrated in FIG. 7, since the length of the chamfering edge, lb, is substantially longer than the length of the cutting edge, lc, the chamfering edge should also endure considerable load corresponding to a force applied thereto.
In addition, it may be understood that Prior Art 1 is operated in a manner in which the cutting tool cuts the central portion by a predetermined value per every one rotation, and the load received when performing cutting and the load received when performing chamfering are different from each other, i.e., the cutting resistance P variably acts. Here, the cutting resistance P is determined by a specific cutting resistance Ks according to the quality of a material to be cut, a cut width l, and a processed depth dp, and may be expressed by an equation as follows.P=Ks×l×dp 
Accordingly, as illustrated in FIG. 7B, at the time of using a cutting tip for cutting, a pitch may be calculated by estimating the cut width lc and the processed depth dp while neglecting the specific cutting resistance according to the quality of the material to be cut. However, at the time of chamfering, as illustrated in FIG. 7A, because the cut width lb varies depending on the thickness of the pipe material, t, it is difficult to calculate a pitch value (a depth to be processed per one rotation) suitable for chamfering. Due to this reason, the chamfering may not satisfy various processing requirements, which makes commercialization difficult, and the chamfering tool is frequently damaged which may also cause a problem in mechanical design to overcome it.
A gear is engaged with a finger stop such that whenever the gear rotates by a predetermined angle, the cutting tool and the chamfering tool are lowered to perform cutting by a predetermined depth. When it is intended to cut and chamfer a pipe material having a thickness of dozens of mm, there is a problem in that the gear, the accessories below the gear, the finger stop, and so on may be damaged as the gear and the finger stop collide with each other hundreds of times. For example, assuming that the gear has five protrusions, the pitch at the time when the gear makes one rotation is 1 mm, and the thickness of the pipe is 20 mm, the finger stop and the gear will collide with each other 5 times in order to cut 1 mm from the pipe material, and will collide with each other by 100 times in order to process 200 mm. When such a processing is performed 100 times per day, the collision will occur 10,000 times, and when such a processing is performed for 100 days, the collision will occur 1,000,000 times. When such collision occurs during a high speed rotation, a considerably high impulse will be generated, which will exert a very harmful influence on the endurance of the apparatus.
In addition, in Prior Art 1, since the cutting is performed by a predetermined depth only when the finger stop is engaged with the gear, it is impossible to arbitrarily adjust the cutting depth and the range of choice of a workpiece is narrowed. That is, depending on the material of the workpiece or the kind of a tool, the cutting speed, the cutting depth, and so on are determined. However, Prior Art 1 may have a problem in that it cannot adjust the processing conditions even if such processing conditions exist.
In addition, the chamfering angle may vary depending on the kind and design of the pipe material. However, the Prior Art 1 has an inconvenience in that it is necessary to replace the chamfering tool in order to change the chamfering angle.
In order to overcome the problems of the prior art as described above, the inventor of the present application has researched measures that are capable of freely controlling forward and backward movements of a cutting tool, allowing the cutting tool to move not only in a direction perpendicular to a circular material to be cut, but also in an axial direction of the material to be cut so as to enable the processing of various shapes as well as cutting and chamfering, and are capable of simultaneously carrying out cutting and chamfering operations for a heavy pipe, such as a pipe material or a hard-to-cut material, having a thickness of dozens of mm or more.
In particular, the inventor has researched various measures for a method that is capable of freely controlling the movement of a tool within a rotary body. As a result, a first control method based on wireless communication, a second control method based on centrifugal force, and a third method based on hydraulic pressure have been proposed, and finally a control method using a rotational speed ratio have been proposed.
A tool control method based on wireless communication, which is the first proposed technique, is proposed by the applicant and the inventor of the present application in Korean Patent No. 1407327 (registered on Jun. 9, 2014), which is incorporated by reference, a tool control method based on centrifugal force, which is the second proposed technique, is also proposed in Korean Patent No. 1407328 (registered on Jun. 9, 2014), which is incorporated by reference, a tool control method based on hydraulic pressure, which is the third proposed technique, is proposed in Korean Patent No. 1415513 (registered on Jun. 30, 2014), which is incorporated by reference, and a tool control method using a rotational speed ratio is proposed in unpublished Korean Patent Application No. 2014-0066480 (filed on May 30, 2014), which is incorporated by reference.
Representative related techniques for the tool control method using a rotational speed ratio for a plurality of wheels, which is the fourth proposed technique, are as follows.
Prior Art 2: U.S. Pat. No. 5,605,083 (published on Feb. 25, 1997) (title of the invention: pipe cutting apparatus with differential speed rotatable ring cutter actuation), which is incorporated by reference.
Prior Art 3: JP Patent Laid-Open Publication No. 2001-096421 (published on Apr. 10, 2001) (title of the invention: pipe cutting apparatus), which is incorporated by reference.
Prior Art 4: JP Patent Laid-Open Publication No. 2003-117720 (published on Apr. 23, 2003) (title of the invention: pipe cutting apparatus), which is incorporated by reference.
Prior Art 5: EP 2085169A (published on Jul. 11, 2012) (title of the invention: pipe cut-off apparatus), which is incorporated by reference.
Prior Arts 2 and 5 were filed in the name of the invention to propose a method of controlling a movement of a tool according to a speed ratio between a rotary body and a ring gear by mounting the rotary body on the tool and then installing the ring gear, which is relatively rotated in relation to the rotary body, to be interlocked with the tool.
Prior Art 3 proposes a method of controlling a movement of a tool by mounting a plurality of planet gears within a rotary body, mounting a tool on the planet gears, and then causing the rotation of the planet gears to be relatively rotated in relation to the planet gears.
In addition, Prior Art 4 proposes a method of controlling a movement of a tool according to whether the tool is meshed with a specific gear in a two-stage composite gear by mounting a tool on a rotary body and then installing the two-stage composite gear interlocked with the tool within the rotary body.
In sum, it has been found that the prior arts related to the rotational speed ratio are provide with a rotary boy and a relatively rotated control wheel in order to control a vertical movement or a pivotal movement of a tool mounted on a rotary body, and a technique, which was intended to be proposed by the inventor, has already been known by the prior arts.
The items to be newly proposed by the inventor in relation to a tool control method using a rotational speed ratio in an orbital pipe cutting apparatus is related to a technique in which two or more tools are mounted on a rotary body, and then the two or more tools are selectively controlled. Prior Arts 2 to 5 cannot individually control one or more tools neither selectively nor independently.